Background and Aim

Drought is the main abiotic stress affecting Mediterranean forests. Root systems are responsible for water uptake, but intraspecific variability in tree root morphology is poorly understood mainly owing to sampling difficulties. The aim of this study was to gain knowledge on the adaptive relevance of rooting traits for a widespread pine using a non-invasive, high-throughput phenotyping technique.

Methods

Ground-Penetrating Radar (GPR) was used to characterize variability in coarse root features (depth, diameter and frequency) among populations of the Mediterranean conifer Pinus halepensis evaluated in a common garden. GPR records were examined in relation to aboveground growth and climate variables at origin of populations.

Results

Variability was detected for root traits among 56 range-wide populations categorized into 16 ecotypes. Root diameter decreased eastward within the Mediterranean basin. In turn, root frequency, but not depth and diameter, decreased following a northward gradient. Root traits also varied with climatic variables at origin such as the ratio of summer to annual precipitation, summer temperature or solar radiation. Particularly, root frequency increased with aridity, whereas root depth and diameter were maximum for ecotypes occupying the thermal midpoint of the species distribution range.

Conclusion

GPR is a high-throughput phenotyping tool that allows detection of intraspecific variation in root traits of P. halepensis and its dependencies on eco-geographic characteristics at origin, thereby informing on the adaptive relevance of root systems for the species. It is also potentially suited for inferring population divergence in resource allocation above- and belowground in forest genetic trials.

中文翻译：

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探地雷达作为表征广泛针叶树根系性状种内变异的表型工具

背景和目标

干旱是影响地中海森林的主要非生物胁迫。根系负责吸水，但由于取样困难，人们对树根形态的种内变异知之甚少。本研究的目的是使用非侵入性、高通量表型分析技术，了解广泛分布的松树生根性状的适应性相关性。

方法

探地雷达 (GPR) 用于表征在普通花园中评估的地中海针叶松 halepensis种群之间粗根特征（深度、直径和频率）的变异性。GPR 记录与地上生长和人口起源处的气候变量有关。

结果

在分为 16 个生态型的 56 个范围广泛的种群中检测到根性状的变异性。在地中海盆地内，根直径向东减小。反过来，根频率，但不是深度和直径，随着向北的梯度下降。根性状也随起源的气候变量而变化，例如夏季与年降水量的比率、夏季温度或太阳辐射。特别是，根频率随着干旱而增加，而对于占据物种分布范围热中点的生态型，根深度和直径最大。

结论

GPR 是一种高通量表型分析工具，可以检测P. halepensis根特征的种内变异及其对原产地生态地理特征的依赖，从而了解根系对物种的适应性相关性。它还可能适用于推断森林遗传试验中地上和地下资源分配的种群差异。